In four-wheel drive vehicles with both two-wheel drive and four-wheel drive modes, some means must be provided for disengaging one axle (typically the front axle) from the drive train when operating in two-wheel drive mode. Operation in the two-wheel drive mode is generally more efficient for safe, on-road driving conditions, and in a "part-time" system with no inter-axle differential, two wheel drive mode is the normal mode for travel on dry, hard surface roads.
One method of allowing the wheels of the non-driven axle to rotate free of the drive train in two-wheel drive mode is to provide each of the wheels with manual locking hubs. For example, the U.S. Pat. No. 3,414,096 of Reed discloses locking hubs which allow the front wheels to rotate independently of their associated axle. In order to lock or unlock the hubs, the driver of the vehicle must get out of the vehicle and manually turn a control on each hub to its locked or unlocked position, respectively.
Another method of adapting to two-wheel drive mode is for the driver to use a manual shift lever in order to allow at least one of the wheels to rotate free of the axle. For example, the U.S. Pat. No. 1,440,341 of Crispen discloses an axle having one side which can be disconnected by a system in which a shift fork controls movement of a clutch collar or sleeve to selectively connect or disconnect spindle sections of the axle. After disconnection, one of the wheels is free to rotate while the other is driven from a source of power. Likewise, the U.S. Pat. No. 2,913,929 of Anderson discloses a front axle double disconnect mechanism actuatable by a movable lever located in the passenger compartment of the vehicle. The movable lever is connected through linkage to complementary clutch collars which are shiftable between four-wheel drive and two-wheel drive positions on the left and right axle shafts. In the U.S. Pat. No. 2,770,150 of Culverwell a front axle design for a four-wheel drive vehicle includes a mechanism for simultaneously connecting or disconnecting the right and left axle shafts to a center differential. The connection takes place while shifting complementary clutch collars located within the front differential housing. The U.S. Pat. Nos. 1,284,759 to Paxton and U.S. Pat. No. 3,058,558 to Hawk disclose disconnect mechanisms adjacent the wheels of a vehicle for changing vehicle operation between four-wheel drive and two-wheel drive. Each disconnect mechanism includes a shiftable clutch collar.
Other disconnect mechanisms of the type to which this invention relates are disclosed by the U.S. Pat. Nos. 2,384,781, of Rockwell et al. 3,552,516, to Beard et al., 3,522,861 to Middlesworth et al and 2,084,406 to Morgan.